Catalytic reduction of carbon oxide by hydrogen



Patented Jan. 30, 1951 CATALYTIC REDUCTION OF CARBON OXIDE BY HYDROGEN Walter G. Frankenburg, Miliersville, la., assignor to Hydrocarbon Research, Inc.,

New York,

N. Y., a corporation of New Jersey No Drawing. Application April, 30, 1947, Serial No. 745,115

' lClalm.

The present invention relates to the synthetic production of hydrocarbons, oxygenated hydrocarbons, and the like by the catalytic reduction of carbon monoxide with hydrogen. More particularly, it is concerned with conducting this reaction through the agency of new and improved catalysts.

It has been previously proposed to cause the interaction of carbon monoxide and hydrogen through the agency of catalysts comprising metals of group 8 of the periodic table particularly metals of the iron group and ruthenium. Of these, cobalt and iron have been most successfully employed. They are characterized by a relatively good selectivity being capable under optimum temperatures and pressures of producing a predominance of hydrocarbons and oxygenated hydrocarbons in relatively narrow predetermined boiling ranges. While, for example,

when operating to produce hydrocarbons predominantly in the motor gasoline range, there is an undesirable production of lighter gaseous hydrocarbons as well, nevertheless this undesired product is not excessive in quantity if optimum conditions of reaction are maintained. A tend-. eney, moreover, particularly in the case of the iron catalyst, to consume carbon monoxide in the production of by-product carbon dioxide instead of desired by-product water vapor can also be overcome, to some extent, by proper operation. It is an object of the present invention to provide a new group of catalysts which, per se, are eifective for the catalytic synthesis of hydrocarbons, oxygenated hydrocarbons and the like, and provide an active catalytic medium broadly equivalent to the known catalysts discussed above and, in some particulars, superior. Another obiect contemplates a process as above wherein the reaction may be carried out with a reasonably low production of undesired byproducts, particularly carbon dioxide and methane. Other objects will beapparent from the following specification and claims.

In accordance with the present invention a fresh feed gas consisting essentially of hydrogen and carbon monoxide advantageously in about combining proportions, is passed in contact, under reaction conditions, including an'elevated temperature and preferably although not necessarily, elevated pressure,'with a catalyst comprising a carbide of an element selected from the class consisting of titanium, vanadium, chrmium, manganese, zirconium, columbium, molybdenum, masurium, hafnium, tantalum, tungsten, rhenium, thorium, protoactinium The foregoing class of elements comprises the elements of groups IVA, VA, VIA and VIIA of the periodic table. More specifically, these elements include all of the transition elements in.

which an incompleted subshell or orbit of electrons just within the outer partially completed shell, contain from 2 to 5 electrons inclusive. In view of the many current variations in interpretations, and periodic arrangement of the elements, reference herein to the periodic table is specifically intended to mean Mendeleeils Periodic Table as set forth on page 411 of the Text- Bcok of Inorganic Chemistry by Partington (fifth edition).

It has been discovered that the said carbides of the elements in question are active for catalyzing the reaction of carbon monoxide and hydrogen, whereby hydrocarbons and oxygenated hydrocarbons are formed. It has furthermore been discovered that ,the catalystic action, in general, proceeds, at appropriate temperatures, with the activation of the carbon monoxide to such an extent relative to the activation of the hydrogen as to promote the formation of normally liquid hydrocarbons in preference to normally gaseous hydrocarbons. In short, it appears that the catalysts in question have a general tendency to predominantly activate the carbon monoxide for the production of hydrocarbons while relatively restricting the hydrogenating eileet so that polymerization of nascent CH: units tends to precede the hydrogenation of individual or only partially polymerized CH: groups which would otherwise result in the formation of material proportions of hydrocarbon gases.

Moreover, carbon dioxide production is usually moderate, and in some cases more limited than that characterizing the earlier proposed catalysts. It is to be understood, however, that the foregoing theories are advanced only for the purpose of better illustrating the principles involved and are not intended as a limitation herein.

In any event, the invention has the advantage of providing a process which materially limits the relative production of gaseous hydrocarbons, and tends toward the production of by-produet water vapor in place of carbon dioxide, with the resulting conservation of carbon supplied to the process.

The catalysts in question may be employed individually or in combination, or together with other previously proposed catalysts and activators for the present process. In general the cataand uranium. as lysts taught by the present invention when used.

per se, embody numerous advantages including those mentioned above. On the other hand, in combination with conventional catalysts they may tend, progressively, to modify the usual effects in accordance with their individual characterlstics so that quantitatively intermediate results may be achieved. In short, the catalysts of the present invention may be combined with typical iron and cobalt catalysts. For example, a suitable product comprising tungsten carbide in combination with a typical iron catalyst may be prepared by dissolving tungsten carbide in molten iron and comminutlng the resultant prod uct. Alternatively, an iron-tungsten alloy containing a substantial proportion of tungsten may be formed into a carbide by the well known technique of cemented carbide formation. n the other hand, a pure tungsten carbide by itself or with suitable promoters or activators, is, per se, active and valuable as a catalyst in the present process. Other carbides of the elements in question, such as zirconium carbide, vanadium carbide, chromium carbide, manganese carbide, thorium carbide and uranium carbide are equally suitable as such or associated in any convenient way with an iron, cobalt, nickel or ruthenium catalyst of the type hitherto proposed.

In general the reaction in question proceeds at elevated temperatures below 1000 F. considering broadly the entire field of catalysts disclosed. It is to be understood however that the optimum temperature in each case is a characteristic best determined by trial for each specific catalyst. In general it may be stated that, in each case, the optimum range for the production of liquid hydrocarbons boiling in the gasoline range will usually be between 400 and 700 F. and typically at a temperature about intermediate between the two. For example, tungsten carbide is efiective as a catalyst at about the range characteristic of the typical iron catalyst for the reaction in question, making it quite suitable as a component of a combination catalyst including the aforementioned catalytic iron. By itself, somewhat higher temperatures may be desirable, for example 650 F. or thereabouts, and broadly in the range of 500 to 750 F. The optimum temperature for uranium carbide is similarly about 650 F. Similar remarks apply to the case of the vanadium or thorium carbide. As, however, in the case of any specific catalyst for the present process, the narrow, truly optimum temperature can only be actually determined by the usual, conventional procedure, namely trial of a test sample.

Pressures are similarly determined, although these do not appear to be highly critical since reaction proceeds generally in the range of atmospheric up to 500 pounds per square inch or higher. Usually the optimum pressures will be somewhat elevated, as for example, 100 to 300 pounds per square inch. Here again the optmum pressure, in common with hitherto known catalysts, will vary not only with the particular catalyst, but in accordance with the specific product desired. Also, by selection of temperature and pressure, some degree of flexibility is available in regard to directing the process toward predominant production of oxygenated hydrocarbons, or hydrocarbons free from oxygen atoms as may be desired. Similarly the selection of appropriate temperatures, in particular results in reaction products of predetermined average molecular weight. That is tosay, for instance, higher temperatures than those indicated above usually result in hydrocarbons or oxygenated hydrocarbons of lower molecular weight, while conversely lower temperatures, tend toward products of higher molecular weight.

Contact time is similarly determined, and in most cases is not critical, the reaction going forward rapidly under conditions of good temperature control and under low or high space velocity as may be desired.

The apparatus which may be employed will not be described in detail here for the reason that it may follow the design of any of the typical processing equipment hitherto known and proposed for the catalytic synthesis of hydrocarbons by the reduction of carbon monoxide with hydrogen. One arrangement which has been found suitable involves passing of the reactant gases upwardly through a mass of powdered catalyst maintained in a state of dense phase fiuidization thereby, with suitable cooling surfaces immersed in the fluidized mass and maintained at an appropriate temperature such that the catalyst bed has a uniform predetermined temperature throughout corresponding to the desired reaction temperature.

The feed gases may consist of any of the usual compositions for the reaction in question containing essentially hydrogen and carbon monoxide, generally in the ratio of approximately 2:1. On the other hand, the proportioning of the reactants is not critical and may be varied widely insofar as both of the essential reactants are present in the initial feed in an amount sufiicient to form the desired products. This means that any other usual components of synthesis gas may be present either as inerts or for their usual additive function, although preferably in minor or limited proportion. Such for instance are methane, carbon dioxide, nitrogen and the like.

In accordance with one specific embodiment submitted in order to illustrate the specific practice of the present invention in greater detail, a mass of tungsten carbide in the form of a powder passing through a 325-mesh screen is placed in a reaction vessel and a reactant gas comprising about 64% hydrogen and about 32% carbon monoxide is passed upwardly therethrough at a linear velocity of about 1.5 feet per second to maintain the carbide in a condition of dense phase fluidization.

Temperature is maintained at 650 F. within the mass of catalyst by suitable cooling surfaces immersed therein, and the eiiiuent gases removed from the upper surface of the fluidized mass of catalyst are cooled to 70 F. and subjected to separation to remove normally liquid products.

The normally liquid products are permitted to gravitate into a water layer and an oil layer. The oil layer, comprising predominantly liquid hydrocarbons boiling in the motor gasoline range, corresponds overall to about of the carbon monoxide converted in the reaction. The gaseous products separated from two liquid layers contain carbon dioxide corresponding to about 5% of the converted carbon monoxide, and gaseous hydrocarbons corresponding to about 12% of the converted carbon monoxide. The other 8% of the converted carbon monoxide goes into oxygenated products.

In another example, otherwise the same as the first above mentioned, the tungsten carbide is substituted by a mass of powdered catalyst consisting of iron and tungsten carbide formed parts of iron and tungsten. In this case the yield of liquid hydrocarbons drops to the region of 65% based on the converted carbon monoxide and carbon dioxide occurs in the efiluent gases in an amount equivalent to about 10% of the converted carbon monoxide.

From the foregoing it will be apparent that the present invention provides a new and improved process and catalyst for the formation of hydrocarbons, oxygenated hydrocarbons, and the like by the catalytic reduction of carbon monoxide with hydrogen. -Whi1e disclosed above essentially in the unsupported state, these catalysts are equally adaptable to embodiment with the conventional carriers, such as diatomaceous earth, filter-eel and the like, and may be deposited and prepared thereon in any conventional manner.

Obviously many modifications and variations of the invention as hereinafter set 'forth may be made without departing from the spirit and scope'thereof, and therefore only such limitations should be imposed as are indicated in the appended claim.

I claim: v

A process for the production of normally liquid hydrocarbons which comprises passing a mixture consisting essentially of hydrogen and carbon monoxide into a reaction zone into contact with a catalyst consisting essentially of a tungsten carbide at a temperature within the range of from about 400 to about 700 F. and at a pressure within the range of from about atmospheric to about 500 pounds per square inch, and recovering liquid hydrocarbons, from the resulting .products of reaction.

WALTER G. FRANKENBURG.

REFERENCES OCITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTH R REFERENCES Hodgman et al., Handbook of Chemistry and Physics, 27th ed., 1943 (pages 484-485), Chemical Rubber Pub. Co. 

